This invention relates to under floor insect control methods for residential structures, especially a method to protect wooden structures from termites and other wood-decaying injurious insects.
In conventional termite control methods for wooden structures, insect control chemicals containing emulsions or liquid concentrates are sprayed on the under floor soil and on the column surfaces of structures. These methods, however, do not permanently immobilize the insect control chemicals and do not provide prolonged insect control effects because the insect control ingredients evaporate in a relatively short time period. In order to improve permanent immobilization, certain insect control methods have been developed. For instance, in one method a hardened resin foam coated isolation layer, a barrier layer, containing an insect control chemical is formed by forcefully mixing a main solution (the asphalt emulsion modified polyvinyl acetate resin emulsion, which is a mixture of polyvinyl acetate resin emulsion and asphalt emulsifiable concentrates at about 7:3 proportion) containing an insect control chemical and an organic solvent solution (in which hydrophilic low molecular weight polyurethane resin is dissolved by methyl ethyl ketone or other organic solvents). The mixture is then sprayed on the structure's under floor soil surface.
Asphalt emulsion concentrate is a highly viscous black colored material and the main solution in the above instance, the asphalt emulsion modified polyvinyl acetate resin, is also black. The equipment and tools for spraying this mixture are quickly blackened and dirtied. Operators must be extremely careful when handling and spraying the mixture because their work clothes cannot be cleaned completely if soiled by the mixture. Therefore, work efficiency is significantly reduced. Asphalt emulsion concentrate, because it is usually a cationic surface active agent-based oil-in-water type emulsion formula, is susceptible to emulsion destruction when in contact with an anionic surface active agent. Therefore, it causes condensation and separation of emulsified-dispersed asphalt. Thus, it significantly restricts the choice of emulsion concentrate used for aqueous polyvinyl acetate resin emulsion. In addition, asphalt is principally composed of hydrocarbons and thus melts rubber packing and other materials used in the spraying equipment and tools. And, polyvinyl acetate emulsion increases the viscosity of added asphalt emulsion, thus making handling of the main solution more difficult.
The mixed resin foam coating layer formed by mechanically and forcefully mixing the asphalt emulsion modified polyvinyl acetate resin and organic solvent solution of hydrophilic polyurethane resin and by spraying it embeds and immobilizes the insect control ingredient which is mixed and sprayed together. The dried coating layer thereby formed, however, gradually contracts over time apparently due to the property of asphalt emulsion and creates, for instance, cracks and gaps several years later. The performance of the layer at that point is significantly reduced and the insect control effects are greatly diminished.
The inventors of this invention have repeatedly test produced various synthetic resin based aqueous emulsions and conducted application experiments to devise methods to solve the above mentioned problems. They have paid special attention to materials that can replace the asphalt emulsion. As a result, the inventors discovered that the mixed resin foam layer keeps the insect control chemical stable and immobilized for a long time period, allows little contraction over time, and effectively prevents cracks even if a slight contraction occurs because of the flexibility of soft to semi hard polyurethane resin. This layer is formed by spraying, along with an insect control chemical, a mixture of an aqueous emulsion, which is a copolymeric resin of a methacrylic ester based monomer and vinyl acetate (hereinafter referred to as "main solution"), and an organic solvent solution made of a polyurethane resin forming diisocyanate and polypropylene glycol.